Aircraft undercarriage

ABSTRACT

The undercarriage has two pairs of coaxial wheels disposed in tandem, and one of these pairs (rear or front) is orientable about a vertical axis, due to an articulation. A telescopic shock absorber is incorporated in that articulation.

United States Patent Inventor Pierre Joseph Martin Lallemant Port-Marly, France Appl. No. 774,902 Filed Nov. 12, 1968 Patented Jan. 19, 1971 Assignee Societe Hispano-Suiza-Lallemant Bois, Colombes Priority Nov. 14, 1967 France 128,176

AIRCRAFT UNDERCARRIAGE 2 Claims, 5 Drawing Figs.

US. Cl 244/ 104, 244/50 Int. Cl ..B64c 25/50, B64c 25/5 8 Field of Search 244/ 100, 104, 102, 103, 50

References Cited UNITED STATES PATENTS Breguet Spaeth..... Eldred Nichol] Westcott, Jr. Knights et al FOREIGN PATENTS France Great Britain Primary ExaminerMilton Buchler Assistant Examiner-Paul E. Sauberer Attorney-Larson, Taylor and Hinds 244/ 104 244/ 104X 244/ 104 244/ 104X 244/ 103 244/ 104X ABSTRACT: The undercarriage has two pairs of coaxial wheels disposed in tandem, and one of these pairs (rear or front) is orientable about a vertical axis, due to an articulation. A telescopic shock absorber is incorporated in that articulation.

PATENTED JAN 1 9 l97l SHEU 3 0F 5 1 AIRCRAFT UNDERCARRIAGE This invention relates, in a general manner, to tandem undercarriages for aircraft, the word tandemf signifying that the undercarriage (or the right or left undercarriage element when it concerns, as is generally the case, a principle undercarriage) comprises at least two wheels (or groups of coaxial wheels) disposed one behind the other in the longitudinal direction (this disposition being called in tandem") and connected to a support leg by the intermediary of an articulated device having at least one rocker arm permitting vertical movements of said wheels against the action of shock absorber means. The invention is more particularly. but not exclusively, concerned. among these undercarriages, with principle undercarriages of the tandem type invwhich each element (right or left) comprises at least two wheels (or groups of coaxial wheels) disposed in tandem and connected respectively by two distinct rocker arms to the support leg of the undercarriage element considered.

The essential feature of French Pat. No. 1,544,174 of l3th Sept. 1967 consisted, in making each element of the undercarriages of the type in question comprise a leg supporting at least two wheels (or groups of coaxial wheels) in tandem by the intermediary of a device having at least one rocker arm permitting vertical movements of said wheels against the action of shock absorber means, and in interposing, between the device having at least one rocker arm and one (front or rear) of these two wheels (or groups of coaxial wheels), an articulation having a vertical axis permitting changes of direction of the wheel considered, this articulation being arranged so that its vertical axis is situated in a zone extending in front of the wheel considered by a longitudinal distance at the most equal to half the radius of the wheel in question and means being provided maintaining the verticality of the axis of this articulation during vertical movements of that wheel.

The present invention is concerned with original constructional features relating to the arrangement of the shock absorber means and of the articulation having a vertical axis of tandem undercarriages established generally in accordance with the principle feature of the above-mentioned prior patent, although in the present invention the zone in which the vertical axis of the articulation is situated is not limited to extending in front of the axis of the wheel considered by a longitudinal distance at the most equal to half the radius of the wheel in question; this zone can extend in front of the axis of the wheel considered by a longitudinal distance equal, for example, to the entire radius of the wheel in question.

According to one of the features of the present invention, the shock absorber means of the undercarriage element considered is constituted by a telescopic shock absorber coaxial with the articulation of vertical axis associated with the orientable wheel (or group of coaxial wheels) of the undercarriage element, this telescopic shock absorber being incorporated at the interior of the articulation of vertical axis,

According to another feature of the present invention, the articulation of vertical axis of the orientable wheel (or group of coaxial wheels) is rigidly connected to the leg of the undercarriage element considered, and this orientable wheel is carried by a rocker connected directly to one end of a balancer articulated on this leg and whose other end is connected to the other wheel (or group. of coaxial wheels) of the undercarriage element.

Other features of the present invention will become apparent from the following description,

The invention can be applied, for example, to the principle undercarriage of an aircraft having a tricycle landing gear.

In any case, the invention will be able to be well understood with the aid of the following complementary description, as well as of the accompanying drawings, which complementary description and drawings are, of course, given merely by way of example.

In these drawings:

FIGS. 1 and 2 represent in lateral view two embodiments of a principle undercarriage element established according to a first feature of the invention;

FIG. 3 represents, in vertical section and on an enlarged scale, a shock absorber shown in exterior view in the two preceding FIGS; and

FIGS. 4 and 5 represent, in the same conditions as FIGS. 1 and 2, two embodiments of a principle undercarriage element to which another feature of this invention is applied.

The following complementary description relates to a principle undercarriage for:'an aircraft. in particular a large aircraft, which is intended to comprise, in addition. a front auxiliary undercarriage; and this description relates more particularly to each elementright or left of this principle undercarriage.

This element comprises, as shown in FIG. I, a leg 3 articulated at its upper end on a tubular crosspiece l3 rotatably mounted on a shaft 4 (oriented for example longitudinally), this leg 3 supporting at least two wheels disposed in tandem, andpreferably, two tandem pairs of coaxial wheels, namely a front pair of wheels 51: and a rear pair of wheels 5b.

Thefront wheels 5:; and the rear wheels 5b are connected to the leg 3 by the intermediary of a device having at least one rocker arm permitting vertical movements of these wheels against the action of shock absorber means which will be described more explicitly hereafter with respect to one of the features of the invention.

Preferably, the device supporting the front wheels 5a and the rear wheels 5b comprises two distinct rockers, namely a front rocker 7a and a rear rocker 7b, both articulated on the leg 3; the movements of these rockers 7a and 7b are conjugated by a secondary balancer 8 articulated at 9 on the leg 3 and having its respective ends connected to one of the rockers by a rod and to the other rocker by a console 10 which will be described more explicitly hereafter.

Advantageouslythe wind-bracing of this kinematic structure can then be ensured by an articulated system formed by 7 two rods 11 and 12 connecting the leg 3 to the tubular crosspiece 13, the articulation 14 of these rods 11 and 12 being maintained by a tie rod 15 connecting that articulation to the leg 3.

In addition. it is appropriate to damp the oscillations of the balancer 8 by an auxiliary shock absorber l6 interposed between this balancer and the leg 3. This being the case, according to the essential feature of French Pat. No. 1,544,174 mentioned. above, a possibility of orientation of one of the pairs of wheels-either the front pair or the rear pair-of this undercarriage element is provided by arranging the console 10 in the form of an articulation whose axis X-X is vertical and is situated at the level or slightly in front of the axes of the wheel (by a distance at the most equalto half the radius the wheels to be rendered orientable, in the case of the above-mentioned prior French patent, although in the present invention, this distance can be as great as the radius of the wheels in question, though it wound not normally be greater); the axis X-X is maintained vertical by attributing the same length to the rocker associatedwith the wheels in question and to the corresponding arm of the balancer 8.

The articulation of vertical axis X-X can then be con stituted by rotatably mounting in the'console 10 a tubular shaft 17 angularly fixed, by a compass 101, to a hub 102 sup porting the pair of orientable wheels.

As indicated in the above-mentioned French patent, it is ad vantageous to provide, in addition, locking means permitting the articulation which has just been described to be blocked in the straight ahead position (in particular for landing and taking off); these locking means can advantageously be constituted, by providing, at the upper part of the rotatable tubular shaft 17, external flutes 17b coacting with a slidable sleeve 18 fluted interiorly and carrying at its base a crenellation 18a engaging, when the slidable sleeve 18 is in its lower position (position illustrated in FIG. 1). with a complementary crenellation provided at the upper end of the nonrotatable tubular console 10, and by making some control means eoact with the slidable sleeve 18, for permitting an upward displacement to be imposed on this sleeve, thus disengaging its crenellation 18a and permitting the rotary movement of the sleeve in question, and consequently the turning of the wheels coupled to the sleeve by the compass 101', these control means can be constituted. for example, by a hydraulic jack operated by an electrovalve (not shown).

It should be noted that the crenellation which hasjust been described can be arranged so that the locking of the pair of orientable wheels can only take place for the straight ahead position of this pair of wheels, thus rendering impossible any improper locking of this pair of wheels in a turned position.

FIG. 1 illustrates an embodiment in which the pair of orientable wheels is the pair of rear wheels b.

FIG. 2, in which the same structural elements can be found as in FIG. 1, illustrates another embodiment, in which the pair of orientable wheels is the pair of front wheels 5a, the same reference numerals designating, in FIG. 2, the same elements as in FIG. 1. This concordance of the structural elements and their reference numerals thus renders unnecessary a detailed description of the embodiment illustrated in FIG. 2.

In any case, that is to say both for the embodiment illustrated in FIG. 1 and for the embodiment illustrated in FIG. 2, the principle shock absorber means of the undercarriage element considered, are constituted, according to a feature of the present invention, by a telescopic shock absorber 6, preferably hydraulic, coaxial with the tubular console forming the nonrotatable external element of the articulation of vertical axis XX, this telescopic shock absorber 6 being incorporated in the tubular console.

This feature constitutes an advantageous simplification of the structure of the undercarriage due .to the fact that the shock absorber 6 no longer forms a supplementary external element complicating the problem of the retraction of the undercarriage.

Although the hydraulic shock absorber 6 can be arranged in many ways, taking into account what has just been said, it seems more particularly advantageous to use the embodiment illustrated in FIG. 3, according to which the movable element of the shock absorber is constituted by a cylinder (designated by the reference 6) carrying at its lower end the hub 102 and serving as guide for a plunger piston 103 articulated, by a rotary joint 104, on a cover 105 fixed to the upper end of the rotatable tubular shaft 17, whereby this plunger piston 103 is driven in rotation by friction by the rotating tube 107, and accordingly, does not undergo any relative rotation movement with respect to the cylinder 6 when this cylinder is driven in rotation by the rotating tube 17 by the intermediary of the compass 101.

There will now be described, with reference to FIGS. 4 and 5, two embodiments of a second feature of the invention, independent from the first feature described with reference to FIGS. 1 to 3; FIG. 4 relates to a tandem undercarriage element in which the pair'of orientable wheels is the pair of rear wheels 5b, whereas in the case of FIG. 5, it is the front wheels 50 that are orientable.

The same references designate, in FIGS. 4 and 5, the same elements as in FIGS. 1 and 2.

According to the above-mentioned second feature of the invention, the console 10 maintaining the rotatable elements of the articulation of vertical axis permitting changes of direction of the orientable wheels (rotatable elements comprising in particular a shaft 17 with flutes 17b and a blocking sleeve 18 with a crenellation 18a such as described with reference to FIGS. 1 and 2) is rigidly fixed on the leg 3 instead of being connected to that leg by an articulated parallelogram as was the case for the undercarriage element illustrated in FIGS. 1 and 2, and the pair of orientable wheels (rear wheels 5b in the case of FIG. 4 and front wheels 5a in the case of FIG. 5) is carried by a rocker (rear rocker 7/7 for FIG. 4 and front rocker 7a for FIG. 5) articulated on an arm 106 inclined (from the top towards the bottom and from the rear towards the front) and rigid with the base of the rotatable shaft 17 of the articulation. this rocker being connected directly. preferably by rods I07 passing through the articulation including the rotatable shaft 17, to one of the ends of the balancer'8, whose other end is then connected, by a principle shock absorber 6a. to the rocker (front rocker 7a in the case of FIG. 4 and rear rocker 7b in the case of FIG. 5) carrying the pair of orientable wheels.

In this manner, when the orientable wheels are blocked in the straight ahead position by the crenellated sleeve 18, the torsion forces imposed on the structure of the undercarriage in case of skidding of these wheels, are transmitted directly to the leg 3 by the console 10 forming part of that leg, whereas, in the case of FIGS. 1 and 2, the torsion forces in question are transmitted by the intermediary of a deformable parallelogram whose axes of articulation work in conditions dangerous for their longevity; such a risk could only be attenuated by overdimensioning the axes in question, which would lead to a prohibitive increase of the weight of the undercarriage.

Although this invention has been described with reference to particular embodiments, the invention should not .be limited to these embodiments, since many modifications and changes are possible without departing from the spirit or scope of the invention.

Iclaim:

1. A tandem element of an aircraft undercarriage, comprising:

a leg which supports at least two wheel groups, namely a front wheel group. and a rear wheel group, each group comprising, disposed for rotation about an axis of rotation, at least one wheel, the axis of rotation of the front wheel group being disposed in front of the axis of rotation of the rear wheel group;

said two wheel groups being supported by said leg via the intermediary of rocker means having at least one rocker arm permitting vertical movement of said wheel groups against the action of shock absorber means;

an articulation having a vertical axis, interposed between said rocker means having at least one rocker arm and one of said two wheel groups, control means arranged to coact with said articulation thereby rendering said one wheel group orientable;

said articulation having its vertical axis situated in a zone extending in front of the axis of rotation of said orientable wheel group by a longitudinal distance at the most equal to the radius of said orientable wheel group;

means for preserving the vertically of the axis of said articulation during vertical movement of said orientable wheel group; and

wherein said shock absorber means comprise a telescopic shock absorber coaxial with said articulation, said telescopic shock absorber being incorporated at the interior of said articulation.

2. A tandem element of an aircraft undercarriage, according to claim 1:

wherein said articulation of vertical axis comprises a console; and

wherein said telescopic shock absorber comprises a rotatable tubular shaft mounted in said console, and a movable element in the form ofa cylinder mounted in said tubular shaft, said cylinder carrying at its lower end a hub for said orientable wheel group and serving as guide for a plunger piston articulated, by a rotary joint, to the upper end of said tubular shaft. 

1. A tandem element of an aircraft undercarriage, comprising: a leg which supports at least two wheel groups, namely a front wheel group and a rear wheel group, each group comprising, disposed for rotation about an axis of rotation, at least one wheel, the axis of rotation of the front wheel group being disposed in front of the axis of rotation of the rear wheel group; said two wheel groups being supported by said leg via the intermediary of rocker means having at least one rocker arm permitting vertical movement of said wheel groups against the action of shock absorber means; an articulation having a vertical axis, interposed between said rocker means having at least one rocker arm and one of said two wheel groups, control means arranged to coact with said articulation thereby rendering said one wheel group orientable; said articulation having its vertical axis situated in a zone extending in front of the axis of rotation of said orientable wheel group by a longitudinal distance at the moSt equal to the radius of said orientable wheel group; means for preserving the vertically of the axis of said articulation during vertical movement of said orientable wheel group; and wherein said shock absorber means comprise a telescopic shock absorber coaxial with said articulation, said telescopic shock absorber being incorporated at the interior of said articulation.
 2. A tandem element of an aircraft undercarriage, according to claim 1: wherein said articulation of vertical axis comprises a console; and wherein said telescopic shock absorber comprises a rotatable tubular shaft mounted in said console, and a movable element in the form of a cylinder mounted in said tubular shaft, said cylinder carrying at its lower end a hub for said orientable wheel group and serving as guide for a plunger piston articulated, by a rotary joint, to the upper end of said tubular shaft. 